The present invention relates to an emergency standby cooling device for the core of a pressurized water reactor.
The known cooling devices of this types used in reactors generally comprise accumulators filled with pressurized water, which are connected with the primary cooling circuit of the reactor via isolating valves, which are sensitive to a given lower value of the pressure in the primary circuit. The water filling the accumulators is pressurized with nitrogen.
These known devices have a number of disadvantages. Thus, the injection of water from the standby cooling accumulators of the core does not necessarily take place at the most favourable moment. Thus, when the pressure drop in the primary circuit is due to a relatively small fracture of the piping there may be a draining of the primary circuit without an adequate reduction in the primary pressure to bring about the draining of the accumulators. The primary circuit can then be filled by the "high pressure" pumps, however, the latter constitute active systems which may be erroneously manipulated by the operators. In addition, the draining of the accumulators is linked with a value of the primary circuit pressure and not a vessel level, which is the most significant physical magnitude of the need for filling the primary circuit with water.
Moreover, the injection of water into the primary circuit is generally terminated by an injection of nitrogen serving to pressurize the water in the accumulators. This gas can then be trapped either in the inverted U-tubes of the steam generators, or in the upper parts of the hot branches of the primary circuit when the steam generators are of the "single pass" type, in which the primary fluid enters the generator at its upper end and leaves it at its lower end. Thus, in both cases, there is a loss of efficiency of the cold source constituted by the steam generators.